IS

TRANSMITTERS OF DAMPED OSCILLATIONS 179

located at the anti-node of current m the antenna, then Ix airoroxi

= ' p "

mately = L\ and

i.e., the greater the effective capacity, C2, of the antenna, the closer will
be the coupling.
108. Commercial Form of the Braun Tiansmitter.—a. 'Condensers. _
The requirements of the condensers used are:
1. High breakdown, resistance.
2. Small volume, convenient form.
3. Low energy loss due to dielectric hysteresis.
4. No brush discharge.
These requirements are best fulfilled by air, particularly compressed-
air condensers. MARCONI formerly used air condensers at atmospheric
pressure at the Clifden and Glace Bay transatlantic stations, which were
equipped with a tremendous battery of air condensers totalling 1.6 mf,,
and which were charged to a potential of about 80;000 volts. Compressed-
air condensers of the form shown in Pigs. 68 and 69 have been in use by
the Nat. Elec. Sign. Co., on the recommendation of FESSENDEN. The
disadvantage of air condensers lies in the relatively large dimensions
necessitated by the low dielectric constant of air. In this respect con-
densers of good flint glass are preferable. These are used either in the
form of plate condensers, which are submerged in oil to prevent brush
discharge (Du FOREST, F. DUCRETET, E. RoGER156 and apparently also
now in use by MARCONI in his transatlantic stations), or else in the
form of Ley den Jars (the battery of jars shown in Fig. 70 is part of a
TEJLBPUNKBNT station of about 500 km. range). The Eiffel Tower station
has Mosdcki condensers [Art. 396]. 4S
la order to minimize the brush discharge the jars are sometimes
(e.g., as by the Nat. El. Sign. Co.) immersed in oil, or at least they are de-
signed so as to be long and narrow (Telefuriken) and are arranged in
series-parallel combinations. For example, the Nauen station formerly
had three batteries, each consisting of 120 jars in parallel (each battery
having a capacity of about 1.2 mf.), joined in series (Fig. 215).
6. As to the design of the current path of the condenser circuit it is
hardly possible to make any general statements. Fig. 216 shows a
construction of the TELEFDNKEN* Co. As formerly used for a station of
1000 krn. range, it was made of silver-plated copper tubing, some of the
turns being joined in parallel,
In the arrangements illustrated by Figs. 211 and 212, the contacts
A and B are made so as to be movable, allowing a convenient adjustment
of the frequency arid the coupling. Needless to state, the current path